1. Field of the Invention
The present invention relates to systems and methods for managing circulation passages of digital contents.
2. Related Background Art
With the recent progress of streaming technology and data compression technology, the broadband communications have begun to spread rapidly into households, and digital contents of large volumes such as moving pictures and music pieces have begun to be distributed through communications networks. While digital contents have advantages in that they can be readily copied and processed and their quality do not deteriorate, there is a substantial problem in that their copyright may be infringed by the illegal use.
To prevent the problem of illegal use, there is provided a technique in which digital contents are digitally encrypted by a digital key, and the key is distributed to the user/user terminal as a license independently of the digital contents to protect the copyright. When the digital contents are used, the system checks the presence or absence of the license and/or refers to use condition information contained in the license. Only when the use conditions such as the term of validity are met, the digital contents can be used. According to this system, even when the digital contents are illegally copied, anyone who does not have the license cannot use the digital contents. Furthermore, there is a technique in which a characteristic number of each user terminal is embedded in each digital key upon generating the key, in other words, a different digital key is created for each of different user terminals, and distributed, such that even when the digital contents together with the license are copied onto a different terminal, the key cannot be used at the different terminal where the copy has been made, thereby preventing the illegal use of the digital contents.
Also, in accordance with other techniques proposed, copyright information is embedded in digital contents using digital watermarks to detect the illegal use.
For example, in one of the techniques proposed, ID information is embedded as watermark information in contents that may be used in web pages; ID information and use conditions are registered in a use permission data base (DB); and a monitor center compares the ID information embedded in the contents with the ID information and use conditions registered in the use permission data DB to detect the illegal use of the contents.
Also, in another of the techniques proposed, information that specifies contents to be purchased, a contents distributor and an ID number assigned to each of the purchasers are embedded as watermark information in contents data that are to be distributed.
However, the conventional techniques that use licenses as described above are open to possibilities where the license information may be altered, decrypted contents may be illegally distributed, and the like. Also, when the digital contents leak out, there are no means available to specify from where the contents leak out, which makes it difficult to stop the leakage of the contents.
The conventional techniques that use electronic watermarks to monitor the illegal use are capable of monitoring illegal publications of digital contents on the web pages, but cannot monitor the illegal use that takes place where the monitor center cannot access, such as copying the contents among users' terminals. Moreover, although an enormous amount of contents are currently used on the web pages, it is difficult to monitor all of them.